Choosing an instance in AWS or GCP for training a CNN
I can't do a better job at explaining than Jeremy Howard's team did. 

Follow carefully and systematically all the steps put together here.

You can read more about the different types of machines here, about the possible choices of GPUs here and about the regions and zones here.

Follow the fastai course too.
I can't emphasize how good is it.
You can find the lessons in the left panel.

I would recommend you use Colab for experiments as it has a Tesla-K80 and the cloud computing for something that requires more power. 

Hope it helped!